A small number of the forest species of lepidoptera (moths and butterf

Wait: in this case the instruction are clear: you have to go to that line and weaken the conclusion. If then the virus comes to play it depends

The key to answering primary purpose questions is to understand the purpose of each piece of the passage, and determine how these pieces connect to one another. This passage breaks down nicely into paragraphs, so let's go through each one:

• Paragraph 1: The author introduces the idea of population cycles, and then states that attempts to determine the driving force behind these cycles have been "unproductive." These attempts focused on several different factors -- predatory birds and parasites, changes in habitat, etc.
• Paragraph 2: The author introduces another potential "driving force" -- viruses. He/she then explains the mechanisms behind this theory
• Paragraph 3: The author provides additional support for the theory that viruses are the driving force behind population cycles.

When taken together, it is clear that the author's primary purpose is to introduce and explain the evidence behind a new theory -- the information in the first paragraph is included to provide additional context for the new hypothesis. Let's see how that stacks up against the answer choices in question:


There are a couple of issues with this answer choice. First the author does not refute a "particular theory" -- he/she states that inquiries into several potential theories have been unproductive. In addition, the author's primary purpose is not to refute these other theories. Instead, he/she wants to discuss a new theory (that viruses are the driving force behind population cycles). For these reasons, (B) is out.


Here we go! The "hypothesis" is that viruses are the driving force behind population cycles in lepidoptera. While the author does discuss other theories, he/she includes these in the passage to provide context for the virus hypothesis -- so we can say that the "primary purpose" of the passage is to present the new hypothesis.

I hope that helps!

A Lucid and beautiful explanation as always

GMATNinja VeritasKarishma MentorTutoring



Is the highlighted portion rendering this option incorrect?
This answer choice seems soo correct.
describe new techniques: yes author talks about virus
that may help to determine the driving force behind population cycles in lepidoptera: yes , earlier factors (driving forces mentioned in para-1) did not help to understand population cycles, but virus does.

Hello, adkikani. I would argue that the whole part up to techniques is what makes the answer definitively incorrect, rather than a single word. Keep in mind, a primary purpose question is taking into account the whole passage, not simply the what of its contents, but its authorial presence as well. In this case, describe the development of new techniques begs the question, What are these new techniques, and is the passage describing them, rather than simply presenting them? For this to be the answer, I need to know what these techniques are, and I need to see them permeate the passage, rather than just get a passing mention in one paragraph or another. The nail in the coffin of this answer choice comes from the middle of the second paragraph:

The recent work has been made possible by new techniques of molecular biology that allow viral DNA to be detected at low concentrations in the environment.

I put a finger on these new techniques, but nowhere do I get a description of them, and the passage is certainly not centered on them. Rather, the next sentence lays out the course of the rest of the passage:

Nuclear polyhedrosis viruses are hypothesized to be the driving force behind population cycles in lepidoptera...

Paragraph one presents the issue:

Although many different variables influence population levels, a regular pattern such as a population cycle seems to imply a dominant, driving force. Identification of that driving force, however, has proved surprisingly elusive despite considerable research.

The information in paragraph two above serves to develop the passage from this paragraph one backbone. That is, perhaps the hypothesis that is mentioned is the driving force in question. Altogether, the clues point to (C) as being the hardest answer to argue against. (The question took me 38 seconds to answer correctly. Strong, conclusive, specific language is often easier to debate than more cautious and vague language, and main idea questions in particular tend to prefer the latter.)

I hope that helps. Please let me know if you have further questions.

- Andrew

The passage discusses no technique. Note that the passage introduces the idea that lepidoptera exhibit population cycles and then goes on to say that the driving force has not been identified. Then the passage tells us that new tech has allowed us to see that the agent may be a virus and then it goes on to explain this hypothesis. The only mention of new tech is that it helped discover a probable agent. The whole story is about that agent - the virus, not about the techniques. You would see a lot more mention of scientific methods if tech were discussed.

OE

Q1. It can be inferred from the passage that the mortality caused by agents such as predatory birds or parasites was measured in an attempt to
A. develop an explanation for the existence of lepidoptera population cycles
B. identify behavioral factors in lepidoptera that affect survival rates
C. identify possible methods for controlling lepidoptera population growth
D. provide evidence that lepidoptera populations are self-regulating
E. determine the life stages of lepidoptera at which mortality rates are highest
Inference
The passage states that mortality caused by various agents, birds and parasites among them, was measured because this was the common approach to studying causes of population cycles. This in turn suggests that those scientists engaged in such measuring in the case of lepidoptera were attempting to come up with a definitive explanation for why those lepidoptera population cycles occurred.
A. Correct. Measuring mortality caused by various agents was part of the attempt to determine the driving force behind lepidoptera population cycles.
B. The passage does not indicate that behavioral factors in lepidoptera are related to their mortality as caused by agents such as predatory birds or parasites.
C. The passage is concerned not with controlling lepidoptera population growth, but rather with determining why population cycles occur.
D. According to the information in the passage, scientists sought to measure mortality caused by particular agents in order to determine the driving force behind lepidoptera population cycles. In suggesting that mortality caused by these agents is not that force, the measurements may have indicated that the cycles could be self-regulating, but they were not undertaken in order to provide such evidence.
E. The passage discusses mortality primarily in the caterpillar stage and does not suggest that any research was directed toward comparing caterpillar mortality rates with mortality rates in other life stages of the insects.
The correct answer is A.

Q2. The primary purpose of the passage is to
A. describe the development of new techniques that may help to determine the driving force behind population cycles in lepidoptera
B. present evidence that refutes a particular theory about the driving force behind population cycles in lepidoptera
C. present a hypothesis about the driving force behind population cycles in lepidoptera
D. describe the fluctuating patterns of population cycles in lepidoptera
E. question the idea that a single driving force is behind population cycles in lepidoptera
Main idea
This question depends on understanding the passage as a whole in order to identify its purpose. The first paragraph defines population cycles of lepidoptera and discusses some ways those cycles have been studied. It suggests that a particular agent may regulate these cycles. The second paragraph describes a candidate for this agent: nuclear polyhedrosis viruses. The third paragraph explains why this hypothesis is compelling.
A. The passage mentions new techniques in molecular biology, but it does so in order to explain why a particular candidate for the agent behind population cycles has come to light.
B. The theory the passage presents is that there is a driving force behind lepidoptera population cycles. It does not refute this theory; rather, it offers a convincing case for nuclear polyhedrosis viruses as that force. It also discusses some previous approaches to seeking plausible hypotheses but does not focus on refuting any particular hypothesis.
C. Correct. The passage is primarily concerned with presenting the hypothesis that nuclear polyhedrosis viruses are the driving force behind lepidoptera population cycles.
D. The first paragraph describes the fluctuating patterns of lepidoptera population cycles, but it does so to explain what population cycles are, so that it can then go on to attempt to account for those cycles.
E. The passage is concerned with making a case for nuclear polyhedrosis viruses as the driving force behind at least some lepidoptera population cycles, not with questioning the idea that there is a driving force.
The correct answer is C.

Q3. According to the passage, before the discovery of new techniques for detecting viral DNA, population ecologists believed that viral diseases
A. were not widely prevalent among insect populations generally
B. affected only the caterpillar life stage of lepidoptera
C. were the driving force behind lepidoptera population cycles
D. attacked already declining caterpillar populations
E. infected birds and parasites that prey on various species of lepidoptera
Supporting Idea
This question addresses what the passage states directly about population ecologists’ beliefs regarding viral diseases prior to the discovery of new viral DNA–detection techniques. The second paragraph of the passage states that these ecologists believed viral disease contributed to population decline that was already underway rather than initiating it.
A. The second paragraph states that viral disease had been reported; thus, population ecologists were aware of its existence in insect populations. The passage is consistent with ecologists having believed that it was prevalent.
B. The passage focuses mainly on the caterpillar life stage of lepidoptera, but there is nothing to suggest that scientists held particular beliefs regarding viral diseases’ restriction to that life stage.
C. It is after, not before, the discovery of new techniques for detecting viral DNA when populations ecologists came to believe that such diseases were the driving force behind the population cycles.
D. Correct. As stated in the passage, population ecologists believed that viral diseases contributed to already occurring population decline.
E. The passage does not discuss whether viral diseases may infect any lepidoptera predators.
The correct answer is D.

Q4. According to the passage, nuclear polyhedrosis viruses can remain virulent in the environment only when
A. the polyhedrin protein crystals dissolve
B. caterpillar populations are in decline
C. they are present in large numbers
D. their concentration in a particular area remains low
E. they are sheltered from direct sunlight
Supporting Idea
The passage states in the second paragraph that these viruses remain virulent for many years if they are protected from direct sunlight. They are embedded in crystals of polyhedrin protein.
A. The viruses remain virulent partially because of their being contained in polyhedrin protein crystals.
They would most likely not remain virulent if those crystals dissolved.
B. The viruses remain virulent even when caterpillar populations are not in decline; that is how the viruses initiate new population declines.
C. According to the passage, viral DNA has been detected in the environment at low concentrations, yet the viruses are still virulent. Thus, they need not be present in large numbers.
D. Nothing in the passage indicates that the concentration of these viruses must be low for them to be virulent.
E. Correct. The passage says that if the viruses are protected from direct sunlight, they remain virulent for many years. The context strongly suggests that if they are not so protected, they do not remain virulent.
The correct answer is E.

Q5. It can be inferred from the passage that while inside its polyhedrin protein crystals, the nuclear polyhedrosis virus
A. is exposed to direct sunlight
B. is attractive to predators
C. cannot infect caterpillars’ cells
D. cannot be ingested by caterpillars
E. cannot be detected by new techniques of molecular biology
Inference
The passage indicates that the polyhedrin protein crystals protect the nuclear polyhedrosis virus when it is in the environment. When a caterpillar ingests those crystals, they dissolve. That releases the virus, whereupon it infects the caterpillar’s cells. Thus it is reasonable to infer that the virus must be released from the crystals before it can infect the caterpillar.
A. The passage states that nuclear polyhedrosis viruses remain embedded in polyhedrin protein crystals if protected from direct sunlight, not that the virus is exposed to light when it is in the protein crystals.
B. Nothing in the passage indicates that any organism preys on the virus itself or that it attracts predators to caterpillars that it infects.
C. Correct. The virus must be released from the crystals before it can infect caterpillars’ cells.
D. The passage states that caterpillars ingest the polyhedrin protein crystals.
E. According to the passage, new techniques of molecular biology enable the detection of viral DNA in the environment. The nuclear polyhedrosis virus persists in the environment inside protein crystals.
The passage suggests that the new techniques are able to detect the virus inside its crystals but does not provide any evidence about whether they detect it directly or infer its presence indirectly.
The correct answer is C.



Q6. Which of the following, if true, would most weaken the author’s conclusion in lines 18–22?
A. New research reveals that the number of species of birds and parasites that prey on lepidoptera has dropped significantly in recent years.
B. New experiments in which the habitats of lepidoptera are altered in previously untried ways result in the shortening of lepidoptera population cycles.
C. Recent experiments have revealed that the nuclear polyhedrosis virus is present in a number of predators and parasites of lepidoptera.
D. Differences among the habitats of lepidoptera species make it difficult to assess the effects of weather on lepidoptera population cycles.
E. Viral disease is typically observed in a large proportion of the lepidoptera population.
Evaluation
The sentence in question presents the author’s conclusion that lepidoptera populations may be selfregulating or regulated by something more closely connected to the insects than predatory birds or parasites are. To weaken that conclusion requires weakening its support, namely, that mortality caused by predators and parasites seems not to affect population cycles, and that changing habitats and reducing populations has not altered population cycles either.A. A drop in birds and parasites preying on lepidoptera would not weaken the author’s conclusion; mortality caused by these predators has not affected population cycles.
B. Correct. New experiments involving changes in habitat that did succeed in altering population cycles would suggest that the populations are not in fact self-regulating, and that the search for another cycle-altering agent may be unnecessary.
C. This finding would support the idea that the nuclear polyhedrosis virus is responsible for population
cycles—that is, that the virus is the closely connected agent the author concludes is responsible.
D. The suggestion that the effects of weather may not have been adequately assessed is remotely relevant to the author’s conclusion, but the mere difficulty of assessing the effects provides no positive reason to suppose that weather may be the cause of the cycles. On the other hand, answer choice B does offer evidence for an alternative explanation.
E. Viral disease is what the author ultimately suggests is the agent that drives the lepidoptera population cycles in question. The wide presence of viruses in lepidoptera could help support the author’s conclusion.
The correct answer is B.

What is the LOD of this passage?

My confusion with option C is this - the conclusion states that the cause is not parasite/predator. But we know that virus is present in the parasite/predator itself so hence parasite/predator being the cause for population cycle decrease indirectly. The only logical way of thinking that it is wrong could be that uptil the quoted conclusion - we don't know that virus is the cause for population cycle decrease, but this could still be inferred as a cause via parasite/predator in this choice.

dear AndrewN,
when I reviewed this passage, I missed Q4



I picked up A, because following sentence in the paragraph 2,


would you please clarify what I missed ?

thanks in advance.

Hello, zoezhuyan. You have to be careful in these detail questions to locate the correct details. Notice that the question stem refers to nuclear polyhedrosis viruses [remaining] virulent. The excerpt you quoted from paragraph two simply discusses how the virus is released. It appears as if you may have overlooked the line directly before the one you quoted:


We have a nearly identical match between question stem and answer choice, so (E) must be the answer. You want to simplify your approach to RC detail questions as much as possible. It is not as if the keywords will always match word for word, but most of the time, they do, and in other cases, a few words may be swapped out for synonyms.

I hope this proves helpful to you.

- Andrew

Doesn't the "Predator" in Option B mean the caterpillars since they eat the crystals ?

The problem with (B) is that the question stem suggests that the virus is attractive to predators. But that’s simply not true. At no point is the virus said to be attractive to predators, even if we were to argue that the crystals are attractive to caterpillars.

Also, it seems that the crystals themselves are a protein, likely embedded in the prey of caterpillars. So the crystals themselves are not the prey of caterpillars, and we can eliminate (B).

I hope that helps!

1. It can be inferred from the passage that the mortality caused by agents such as predatory birds or parasites was measured in an attempt to

(You are being asked to infer WHY the mortality caused by agents such as predatory birds or parasites was measured. Remember, you can only infer a piece of information from the content provided in the passage.)

A. develop an explanation for the existence of lepidoptera population cycles This can be inferred from this sentence: “The common approach of studying causes of population cycles by measuring the mortality caused by different agents, such as predatory birds or parasites, has been unproductive in the case of lepidoptera.”

B. identify behavioral factors in lepidoptera that affect survival rates This cannot be inferred. The mortality caused by agents has nothing to do with survival rates

C. identify possible methods for controlling lepidoptera population growth This cannot be inferred. Controlling population growth was not the intention.

D. provide evidence that lepidoptera populations are self-regulating This cannot be inferred. If the populations were self-regulating then the ecologist would not bother finding out about birds or parasites.

E. determine the life stages of lepidoptera at which mortality rates are highest This cannot be inferred. No such indication


2. The primary purpose of the passage is to

(You are being asked WHY the author has written this essay. What was the intention? Remember, the answer cannot contradict what has been mentioned in the passage. Nor can it refer to something that has not been addressed in the passage. The answer also cannot be referring to a small aspect of that was mentioned in the passage; it needs to be more holistic.)

A. describe the development of new techniques that may help to determine the driving force behind population cycles in lepidoptera The technique to detect viral DNA has been briefly referred to, but this is not the primary purpose of the passage

B. present evidence that refutes a particular theory about the driving force behind population cycles in lepidoptera The only theory that has been presented about the population cycles is that it may be regulated by an agent that is more intimately connected with the insect tan are birds or parasites. This fact has been confirmed, not refuted.

C. present a hypothesis about the driving force behind population cycles in lepidoptera The first line of the second paragraph – “Recent work suggests that…” – implies that the researchers are presenting a hypothesis and the first line of the last paragraph says, “one of the attraction of this hypothesis.” this confirms that a hypothesis about the driving force behind population cycles in lepidoptera has been presented.

D. describe the fluctuating patterns of population cycles in lepidoptera It has been mentioned that there are fluctuating patterns in the population cycles. But these patterns have not been described. Even if they had been described, doing so is not the primary purpose

E. question the idea that a single driving force is behind population cycles in lepidoptera As mentioned in Option B, this is not being questioned; it has been confirmed.


3. According to the passage, before the discovery of new techniques for detecting viral DNA, population ecologists believed that viral diseases

(You are being asked what has been mentioned in the passage about what population ecologists believed about viral diseases before new techniques for detecting viral DNA was discovered. Remember, the answer must be stated in the passage; make sure that you don’t choose options that can be inferred.)

A. were not widely prevalent among insect populations generally This has not been mentioned

B. affected only the caterpillar life stage of lepidoptera The passage does not refer to the life stage at which the caterpillar is affected by the virus

C. were the driving force behind lepidoptera population cycles They did not think it was the driving force. They only thought it contributed to the decline.

D. attacked already declining caterpillar populations This has been stated in the second sentence of the second paragraph

E. infected birds and parasites that prey on various species of lepidoptera No such reference has been made.


4. According to the passage, nuclear polyhedrosis viruses can remain virulent in the environment only when

(You are being asked what has been mentioned in the passage about WHEN nuclear polyhedrosis viruses can remain virulent in the environment. Remember, the answer must be stated in the passage; make sure that you don’t choose options that can be inferred.)

A. the polyhedrin protein crystals dissolve This has not been mentioned in the passage.

B. caterpillar populations are in decline This has not been mentioned in the passage.

C. they are present in large numbers This has not been mentioned in the passage.

D. their concentration in a particular area remains low This has not been mentioned in the passage.

E. they are sheltered from direct sunlight The second paragraph says that “if protected from direct sunlight, they may remain virulent for many years in the environment.”


5. It can be inferred from the passage that while inside its polyhedrin protein crystals, the nuclear polyhedrosis virus

(You are being asked to infer WHAT happens when the virus is inside the polyhedrin protein crystal. Remember, you can only infer a piece of information from the content provided in the passage.)

A. is exposed to direct sunlight This cannot be inferred from any sentence in the passage.

B. is attractive to predators This cannot be inferred from any sentence in the passage.

C. cannot infect caterpillars' cells The second paragraph says that “Once ingested by a caterpillar, the crystals dissolve, releasing the virus to infect the insect’s cells.” From this we can infer that the virus cannot infect the caterpillars’ cells unless the crystal dissolves.

D. cannot be ingested by caterpillars This cannot be inferred from any sentence in the passage.

E. cannot be detected by new techniques of molecular biology This cannot be inferred from any sentence in the passage.


6. Which of the following, if true, would most weaken the author's conclusion in lines 18-22?

(The simplified conclusion is that an agent intimately connected with the insect causes population fluctuations. You are being asked to identify which option will show that an agent intimately connected to the agent does not necessarily cause the population fluctuation.)

A. New research reveals that the number of species of birds and parasites that prey on lepidoptera has dropped significantly in recent years This option strengthens the conclusion. Since other potential agents have decreased, this increases the probability that an agent like the virus may be the driving force.

B. New experiments in which the habitats of lepidoptera are altered in previously untried ways result in the shortening of lepidoptera population cycles This introduces new evidence that something else, i.e., the alteration in habitat, may be responsible for the shortening of lepidoptera population cycles.

C. Recent experiments have revealed that the nuclear polyhedrosis virus is present in a number of predators and parasites of lepidoptera. This may be so but this does not change the link between the virus and lepidoptera. We can still say that even if the NP virus is present in the predators, an agent closely connected to lepidoptera is responsible for the short population cycles.

D. Differences among the habitats of lepidoptera species make it difficult to assess the effects of weather on lepidoptera population cycles This option is telling us that although it is possible that weather may affect population cycles or be the driving force, there is no way for us to be sure. This does not definitively weaken.

E. Viral disease is typically observed in a large proportion of the lepidoptera population. This option only tells us a little more about the presence of viral diseases. It doesn’t tell us anything about the causal relationship.

Nitha Jay

GMATNinja VeritasKarishma

Nuclear polyhedrosis viruses are hypothesized to be the driving force behind population cycles in lepidoptera in part because the viruses themselves follow an infectious cycle in which, if protected from direct sun light, they may remain virulent for many years in the environment, embedded in durable crystals of polyhedrin protein.

I have a few SC doubts.
1)What's the role "embedded in durable crystals of polyhedrin protein". Is it a verb-ed modifier? Can you explain the sentence structure?
2)Unable to understand if then condition - if protected from direct sun light, they remain virulent inside crystal - Is my understanding correct?
What will happen if they are exposed to direct sunlight? They will not remain virulent. I am not able to comprehend this sentence correctly. Please help.

Thanks!

No point focusing on SC using CR/RC questions. Language offers a lot of flexibility to authors to sufficiently express matters in every possible context. SC sentences are standalone and still need to make contextual sense to the reader. Hence, they are written with a lot of care. Also, the 5 options are a must because we can only say what is better, not what is correct or incorrect.

As for the role of "embedded...", yes it is past participle modifier. In GMAT SC questions we usually see present participle modifiers at the end of the clause, not past participle. But language allows us to use past participle too to modify the entire previous clause (or subject of previous clause). So would a past participle used this way be incorrect in GMAT SC, I cannot say. We will need to select the best of the 5 options.

2. Yes, if the viruses are protected from direct sunlight, we are told that they remain virulent for many years. If exposed to direct sunlight, it follows that they may or may not remain virulent. We cannot say that they will certainly not be virulent in case of exposure from this limited information. It will likely depend on how long it has been, how long was the exposure etc. All we know is that if protected from direct sunlight (by being embedded in durable crystals of polyhedrin protein), they will remain virulent for long.

Hi,
Can someone please explain in question 2 why option C is correct and not A and also what is the difference between both of them? Also, 1 other question The questions which we get in RC what is the difficulty level for them because gmat is adaptive so if someone marked the wrong answer for question 5 so will that person get the Q6 same as the person who has marked the right answer for Q5 . or the level of question in the RC passage is same for everyone irrespective of the accuracy of their previous answer.